Turtles in time graphic error

[Capoz]

Hi to all

I have an original pcb of turtles in time that give me some glitch error on the sprites

I've done the mask rom test

that test give me no error at the end but during the test when mask rom 15 start I see this



In another forum i read about changing rom 7K and 7L

I've replaced 7K, desoldered the original one, put a socket and then burnt a 27c400, but i've the same error

first of doing it also to 7L, anybody can tell me something more?

thank you to all

Aldo

[Asure]

Mask rom content is copied into ram during the test, this is normal. Test results should come on the screen after that.. what do the tests say?

[Capoz]

Mask rom content is copied into ram during the test, this is normal. Test results should come on the screen after that.. what do the tests say?

Say that's it all ok

But I have alway horizobtal line on the characters

Tomorrow I'll make a video or see the issue.

[Capoz]

Video of the problem

[Asure]

Well, looks like a broken video ram or buffer (74LS245) but can be something else as well. Dry solder joint, or hairline fracture on a trace.. etc.
No RAM errors are reported ever?

Do you have any tools? Multimeter, logic probe, scope.. things like that?

[Capoz]

Well, looks like a broken video ram or buffer (74LS245) but can be something else as well. Dry solder joint, or hairline fracture on a trace.. etc.
No RAM errors are reported ever?

Do you have any tools? Multimeter, logic probe, scope.. things like that?

I have a multimeter

RAM errors where can be detected?

thank you for the help